This application claims priority to Japanese patent application number 2002-31170, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to power tools and more particularly, relates to power tools, such as impact wrenches and impact screwdrivers.
2. Description of the Related Art
Japanese Laid-open Patent Publication No. 7-314344 describes an impact wrench that can be used to firmly tighten fasteners, such as a bolt or a nut. In this type of impact power tool, the tightening torque applied to the fastener may be determined based upon the number of times and the frequency at which the hammer impacts or strikes an anvil. In a known technique, a sensor is utilized to detect impacts between the hammer and anvil. When the number of the impacts by the hammer on the anvil reaches a predetermined number, a motor stops rotating the hammer. Thus, an appropriate amount of torque is applied to the fastener by stopping the tightening operation when the predetermined number of impacts has been reached.
In the alternative, the motor can be automatically stopped after a predetermined time interval or period has elapsed after the detection of the first impact of the hammer striking the anvil. Therefore, an appropriate amount of torque is applied to the fastener.
However, if the predetermined number of impacts or the predetermined interval of time is too high, the tightening torque applied to the fastener will be too great and may damage the fastener. On the other hand, if the predetermined number of impacts or the predetermined interval of time is too low, the tightening torque applied to the fastener will be insufficient. Thus, it is necessary to determine an appropriate number of impacts or interval of time.
The appropriate number of impacts or interval of time varies according to the task to be undertaken due to, e.g., the diameter of the fastener and the material of the workpiece. A reliable method for determining the appropriate number of impacts or interval of time for each different task has not yet been developed. Therefore, an operator has to determine the appropriate number of impacts or interval of time by trial and error. For example, the operator may tentatively set an estimated proper value, undertake the task (tighten the fastener) using the value, and, upon completion of the task, measure the tightening torque in order to determine whether the estimated proper value is appropriate. The operator may then repeat this series of actions in order to find the appropriate number of impacts or interval of time. Therefore, determining an appropriate number of impacts or interval of time requires much time and effort.
It is, accordingly, an object of the present teachings to provide an improved power tool that can save the time and the effort required to determine an appropriate number of impacts or interval of time.
In one aspect of the present teaching, impact power tools may include a hammer that is allowed to slip and rotate freely with respect to an anvil when a force exceeding a predetermined magnitude is applied between the hammer and anvil. Preferably, the hammer may impact or strike the anvil after the hammer has slipped or rotated by a predetermined angle. The impact then causes the anvil to rotate by a small amount and tighten the fastener. Such impact power tools may also include a trigger switch for energizing a drive source, such as an electric or pneumatic motor, and a control device, such as a microprocessor or microcomputer, for controlling the drive source. Preferably, the control device may activate the drive source when the trigger switch is switched to the ON position, and stop the drive source when the trigger switch is switched to the OFF position. Additionally, the control device may measure the number of impacts during the time period from when the trigger switch is switched to the ON position to when the trigger switch is switched to the OFF position. In the alternative, the control device may measure the time period from a first impact to when the trigger switch is switched to the OFF position.
Therefore, an operator skilled at tightening fasteners operates the power tool and, the control device measures the number of impacts or the time period. Generally speaking, a skilled operator is capable of tightening fasteners with an appropriate tightening torque regardless of the task being undertaken. Thus, the measured number of impacts or the time period, is an appropriate number of impacts or interval of time, for stopping the drive source. Accordingly, a novice can utilize the measured number of impacts or the time period in order to apply an appropriate tightening torque to the fastener. This enables even an unskilled operator to reduce the time and effort required to determine the appropriate number of impacts or interval of time for stopping the drive source.
Optionally, a sensor may be provided to detect the impacts between the hammer and anvil. The sensor may communicate detected impacts to the control device and the control device may preferably utilize information concerning the detected impacts in order to control the operation of the drive source. If an oil pulse unit is utilized to generate elevated torque, instead of a hammer and anvil, the sensor may sense some characteristic (e.g., emitted sound) of the oil pulse unit that indicates the oil pulse unit is generating oil pulses. Again, this information may then be communicated to the control device and utilized according to the steps described above and below.
The type of sensor that can be utilized with the present teachings is not particularly limited and may be any type of sensor capable of detecting impacts between the hammer and anvil. For example, the present teachings contemplate the use of accelerometers, which detect the acceleration of the hammer, proximity sensors, which detect the position of the hammer, and/or sound sensors (e.g., condenser microphones, piezoelectric materials, etc.), which detect impact sounds generated by the hammer striking the anvil (or oil pulses generated by an oil pulse unit).
In one embodiment of the present teachings, a display device, such as an indicator or display device (e.g., LED display, LCD display, etc.), may be provided to indicate the measured number of impacts or the time period. The display device may be illuminated or otherwise actuated when the trigger switch is switched from the ON position to the OFF position. Thus, the operator may know the measured number of impacts or the time period.
These aspects and features may be utilized singularly or, in combination, in order to make improved power tools, including but not limited to, impact wrenches and impact screwdrivers. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or, in combination with the above-described aspects and features.